The long term objective of this investigation is to understand how neural systems are constructed, that is, what are the mechanisms and rules which readout information available either in the genes or in the environment into neurons of appropriate number, type, and connectivity? The immediate objective of this project period is to provide an accurate description of what acturally happens in construction of a neural subsystem which performs a specific task during a specific period of an animal's life. This involves answers to the following questions: when are the neurons which compose the system built? How is their mature structure established? How do the cells develop physiologically? When and how is functional connectively within the system produced? What is the role of use or of feedback in achievement of the correct adult output? A careful description of what does happen in construction of such a system should provide strong evidence about the mechanisms and rules of construction, and should eliminate a number of hypotheses. BIBLIOGRAPHIC REFERENCES: Bentley, D. (1975) Single gene cricket mutations: Effects on behavior sensory neurons, and identified interneurons. Science 187: 760-764. Bentley, D. and Hoy, R. (1975) The Neurobiology of Cricket Song. In: Eisner, T. and Wilson, E.O. (Eds.) Animal Behavior. W.H. Freeman and Co., San Francisco.